The present invention relates to copper and copper alloy sheet or foil of significantly improved properties imparted by a novel thin invisible surface coating, and to the method of manufacture of such sheet.
Significant advances in this art have been described in U.S. Pat. No. 3,837,929 issued Sept. 24, 1974 and in related patents such as U.S. Pat. No. 3,677,828 issued July 18, 1972. These disclosures teach the overcoming of difficulties and deficiencies, which were encountered in following earlier teachings, through the provision of a thin glassy surface film of copper phosphate, formed by treatment of the copper or copper alloy substrate with a solution of phosphoric acid or of an alkali phosphate, preceded by or combined with oxidation of the metal surface. The thus-coated metal sheet displayed a desired high resistance to tarnish and other desired properties.
The attainment of these advantages appears to be based, at least in part, on the formation of a glassy pore-free coating of copper phosphate containing polymeric chains including multiple units of phosphorus atoms linked through intervening oxygen atoms in the surface film, which has a thickness of about 20 to 1,000 Angstrom units.
However, such coating has generally been found to effect a significant decrease in solderability, as compared to the clean uncoated metal sheet, such decrease being an important drawback for some uses. For example, such decrease in solderability detracts appreciably from one of the important advantages intended to be provided in treated electrical connector parts, that of the ready soldering to other circuit components.
It is, therefore, a principal object of this invention to overcome such deficiencies by providing a process resulting in a coated copper or copper alloy sheet, wherein the coated sheet displays high values of solderability, while other desirable properties such as substantial resistance to tarnish are also accomplished.
It is a further object to provide a coated copper or copper alloy sheet or foil, and a method of preparing such coated sheet, wherein the solderability of the sheet is maintained at substantially the initial value of the cleaned sheet prior to the treatment.
It is a further object to provide a coated copper or copper alloy sheet or foil, and a method of preparing such coated sheet, wherein initial properties of the sheet are maintained substantially undiminished or are enhanced.
A further object is to provide a process which will efficiently and inexpensively provide such thin surface coating over a copper or copper alloy sheet or foil.
Further objects and advantages of this invention will become apparent hereinafter.